Although the aim of the present study was to examine Shedler and Block’s (1990) provocative claims that adolescent substance experimentation is associated with the healthiest psychological functioning while adolescent abstention and frequent use are both associated with poorer psychological functioning, this study extended their findings and helped fill in existing gaps in the extant literature. Utilizing a large community sample of male and female twins assessed at ages 11, 14, 18, and 21, this study was the first to incorporate all substances—tobacco, alcohol, and drugs—into an a priori substance classification scheme across time (i.e., created abstainer, experimenter, regular user and problem user classifications at ages 11, 14, and 18). Dimensional models of childhood and adolescent personality were used to examine the relations between both antecedent and concurrent personality characteristics and adolescent substance use profiles. Emerging adult outcomes at age 21 were assessed across multiple developmental domains. The role of developmental timing in the relations between substance use profiles and emerging adult outcomes was also investigated. The results for personality suggest that age 18 experimenters tend to have the most adaptive matrix of personality characteristics and problem users the least. Both abstainers and regular users at age 18 had personality characteristics of concern. The results for emerging adult outcomes suggest that substance use profiles have long-term developmental significance. Patterns emerged for each profile that highlighted the importance of examining outcomes across developmental domains while taking into account the role of timing. Despite garnering a substantive amount of support for Shelder and Block’s findings, any substance use was associated with poor emerging adult educational outcomes.